1. Field of the Invention
The present invention relates generally to air routing devices and, more particularly, to air routing devices for providing directional control to helicopters and other aircraft.
2. Description of Related Art
The helicopter 11 shown in FIG. 1 incorporates a direct jet thruster instead of a tail rotor. One prior art reference to Logan et al. (U.S. Pat. No. 4,200,252), issued on Apr. 29, 1980, discloses such a direct jet thruster, the contents of which are incorporated herein by reference. The helicopter 11 includes a main rotor 13, which rotates in a counterclockwise direction about the axis 15 to provide lift. A fuselage 17 is suspended beneath the main rotor 13. The fuselage 17 includes a cabin 19 for housing the pilot and other occupants, a tailboom 21, a main power plant 23, and a transmission 25.
In place of a tail rotor, the helicopter 11 uses a direct jet thruster, which comprises a left opening 31 and a right opening 33. A subsonic low-pressure-ratio fan 27 blows a stream of air into the tailboom 21. The compressed air in the tailboom 21 can be selectively discharged through either a circulation control slot 29 on the right side of the tailboom the left opening of the direct jet thruster 31, or the right opening of the direct jet thruster 33. Pressurized air from the subsonic low-pressure-ratio fan 27 is discharged through the circulation controlled tailboom slot 29 in order to counteract a torque generated by the counterclockwise rotation of the main rotor 13. This counterclockwise rotation of the main rotor 13 tends to push the tailboom 21 toward the right (out of the paper), and the discharged air through the circulation control tailboom slot 29 tends to push the tailboom 21 to the left. The net forces on the tailboom 21 from the main rotor 13 and the discharged air through the circulation control tailboom slot 29 are engineered to cancel each other out.
In addition to being utilized by the circulation control tailboom slot 29, the pressurized air from the subsonic low-pressure-ratio fan 27 can be utilized by the right opening 33 of the direct jet thruster to push the tailboom 21 to the left and cause the helicopter 11 to turn right. The pressurized air from the subsonic low-pressure-ratio fan 27 can similarly be discharged through the left opening 31 of the direct jet thruster in order to push the tailboom 21 to the right and cause the helicopter 11 to turn left. Only one of the left opening 31 and the right opening 33 of the direct jet thruster is open at any given time.
The pilot of the helicopter 11 controls the sizes of the left opening 31 and the right opening 33 of the direct jet thruster with a left foot rudder pedal and a right foot rudder pedal, respectively. When the left foot rudder pedal is completely depressed, the right opening 33 of the direct jet thruster is completely open, and when the right foot rudder pedal is completely depressed, the left opening 31 of the direct jet thruster is completely open. The left foot rudder pedal and the right foot rudder pedal move inversely to one another. Thus, when the left foot rudder pedal is completely depressed, the right foot rudder pedal is not depressed, and when the right foot rudder pedal is completely depressed, the left foot rudder pedal is not depressed.
A conventional air-flow controlling device for the direct jet thruster comprises an inner cylinder having a single opening disposed therein and an outer cylinder having two openings disposed therein. The two openings of the outer cylinder correspond to the left opening 31 and the right opening 33. The outer cylinder is fixed, but the inner cylinder is configured to rotate within the outer cylinder, to thereby move the single opening of the inner cylinder to align with either the left opening 31 or the right opening 33.
As the inner cylinder begins to open either the left opening 31 or the right opening 33, or alternatively, as the single opening in the inner cylinder begins to close either the left opening 31 or the right opening 33, a relatively large vertical component of air exits the aircraft through the respective opening. For example, the single opening in the inner cylinder may be rotated to initially partially open the right opening 33, in which case air from the subsonic low-pressure-ratio fan 27 exits through the right opening 33 in a somewhat vertical direction. As the single opening of the inner cylinder becomes more and more aligned with the right opening 33, the air exiting the right opening 33 develops more of a horizontal force component. This air-flow deflecting device is relatively inefficient in providing crisp directional control to the helicopter 11, especially when high altitude hovering tasks are performed. The initial component of vertical force that occurs with each opening and closing of the left opening 31 and the right opening 33 can have a small negative impact on the handling qualities and stability of the helicopter 11. Additionally, relatively high transmission torque requirements exist with the present conventional device.
The relatively large number of moving parts and the nature and quality of many of these moving parts can be expensive to manufacture. For example, the two concentric cylinders should preferably operate with a low coefficient of friction under a fairly wide range of operating temperatures. Additionally, portions of the inner cylinder, the outer cylinder, and bearings between the inner cylinder and the outer cylinder are all exposed to the outdoor elements, which can reduce operating efficiency and increase maintenance costs.